The present invention relates to a semiconductor laser; and, more particularly, to a 3 dimensional whispering gallery (WG) photonic quantum ring (PQR) laser diode with an ultra-low threshold current.
In general, a surface emitting laser can be classified into either a vertical cavity surface emitting laser(VCSEL) or a concentric circular grating surface emitting laser(CCGSEL), wherein the VCSEL comprises a semiconductor substrate, e.g., n type gallium arsenide, and a VCSEL diode integrated thereon. The VCSEL diode includes a plurality of laterally extending horizontal layers, being arranged one on top of another, in a vertical axial stack including an active cavity region sandwiched between an n type multiple-layer distributed Bragg reflector (DBR) mirror stack and a p type multi-layer DBR mirror stack.
The active cavity region contains a plurality of hole electron pairs forming dipoles along a laterally horizontally extending quantum well. The holes and electrons recombine to emit photons in a process called spontaneous emission. Such photons are emitted in all directions. Numerous reflected trips of such photons back and forth between the DBR mirror stacks ensure to induce stimulated and amplified axial emission, thereby generating an emission of stimulated and amplified axial lasing mode, i.e., VCSEL mode.
A drawback of the VCSEL is that a relatively large injection current is required to reach a lasing threshold. Therefore, the high mean thermal density of the VCSEL has restricted applications. e.g., high density array, optical interconnects and signal processing. Since, further, the wavelength xcexVCSEL in the VCSEL mode increases linearly with temperature, the temperature of the active cavity region of the VCSEL must be maintained with negligible variations.
It is, therefore, a primary object of the invention to provide a photonic quantum ring laser diode with an ultra-low threshold current approaching a xcexcA range.
In accordance with the present invention, there is provided a photonic quantum ring (PQR) laser diode with a plurality of laterally extending layers, one on top of another in the stack axis, comprising:
an active region sandwiched between an n type multi-layer distributed Bragg reflector (DBR) stack and a p type multi-layer DBR stack, wherein, along the circumference of the active region, 3 dimensional PQR radiations are emitted with various wavelengths as a function of slanted view angle with respect to the stack axis;
a covering region for surrounding the active region and for transmitting the three dimensional PQR radiations therethrough, radiation therethrough, whereby said radiation is confined by
wherein the refractive index of the active region is larger than that of the covering region so that the 3 dimensional PQR radiations are confined by a 3 dimensional toroidal Rayleigh""s cavity effectively formed along the circumferential portion of the active region; and fully-connected ring-shaped top electrode in the case of the conventional VCSEL, which make the three dimensional PQR radiations from the active region become visible and detectable.